KR101140513B1 - Dual-mode shared ofdm methods/transmitters, receivers and systems - Google Patents

Abstract

Wireless and network terminals are provided for implementing the new uplink OFDM protocol. In this new protocol, a wireless terminal comprises: a first transmission chain for generating and transmitting low rate mode OFDM transmission in a first frequency band of the OFDM band; And a second transmission chain for generating and transmitting burst mode OFDM transmissions in a second frequency band of the OFDM band, wherein the first frequency band is different from the second frequency band. An access channel is provided that overlays other users' low rate mode transmissions.

Description

Dual-mode shared OPM method, transmitter, receiver and system {DUAL-MODE SHARED OFDM METHODS / TRANSMITTERS, RECEIVERS AND SYSTEMS}

TECHNICAL FIELD The present invention generally relates to wireless communications, and more particularly, to an uplink air interface used in a wireless communications network, and more particularly, to a dual mode shared OFDM method, transmitter, receiver and system. It is about.

A wireless network typically includes an access point through which user equipment (UE) can access the wireless network. Each access point services a softly delineated geographic area, typically known as a coverage area, within which the UE can be used to establish a radio link with a particular access point. That is, within a coverage area corresponding to an access point, a UE can typically expect to be able to communicate (transmit and receive signals) wirelessly with its corresponding access point.

In general, transmissions originating from one or more UEs and transmitted to an access point are collectively known as uplink (to that access point). This is an example of a many-to-one communication system in which multiple UEs must share access to a common wireless channel. It is difficult to manage multi-user access to a common radio channel because each transmission originating from different UEs cannot be easily synchronized in practice. Specifically, in a cellular network, an uplink consists of a number of point-to-point transmissions, all of which are directed to one base station (access point) and by that base station These are originated from respective UEs operating in the cell (coverage area) that are served.

Commonly known as an uplink air interface to control how each UE in a wireless communication network transmits signals to access points (eg, base stations) so that a common wireless channel is effectively shared by multiple UEs. Access methods must be specified and followed. In a cellular network, an uplink air interface must consider transmissions from UEs operating in neighboring cells as well as transmissions from multiple UEs operating within the same cell. That is, a method of dividing a common radio channel, also known as channelization, so that each UE can have transmit access to any portion of the common radio channel for some reasonable amount of time for the radio communications to be effective. This should apply.

Several multi-user access schemes have been developed and used in cellular networks for uplink air interfaces. Examples of such multi-user access schemes include: i) frequency division; ii) time division; And iii) channelization based on code division. According to frequency division multiple access (FDMA), a common radio channel is divided into subchannels, and each subchannel can be dedicated to a single UE. On the other hand, basic time division multiple access (TDMA) allows multiple users to transmit on the entire common wireless channel one at a time. Code Division Multiple Access (CDMA) assigns each UE a unique spreading code (cover) that is orthogonal to all other spreading codes assigned to other UEs, thereby allowing multiple UEs to simultaneously access the entire common wireless channel. Allow to send That is, spreading codes (covers) serve as identifiers or covers included in each of the respective transmissions of the UEs.

The maximum data rate associated with uplink transmissions for each of the foregoing schemes is limited. For example, in 3G (i.e. 3rd generation) cellular networks, based on CDMA, CDMA-specific multiple-access interference limits the data rate to 2 Mbps. Moreover, since different UEs typically do not transmit signals simultaneously, it is difficult to maintain orthogonality between transmissions from different UEs provided by their respective assigned spreading codes. Once the orthogonality between transmissions from different UEs is compromised, multiple access interference is introduced, which limits the maximum uplink data rate. In general, total multiple access interference in a cellular network may consist of intra-cell and inter-cell multiple access interference.

European digital audio broadcast services and some wireless local area network (WLAN) uplink access schemes use a modulation technique known as Orthogonal Frequency Division Modulation (OFDM). OFDM also applies to digital television and is considered a method of obtaining high-speed digital data transmissions that outperform conventional telephone lines. Advantageously, OFDM enables simple processing and high data rate transmission against dispersive channel distortions in broadcast environments and single point-to-point communications. The disadvantage of OFDM is that although it is very effective for broadcast and single point-to-point communication, it does not inherently provide multi-user access.

OFDM has been combined with time division multiplexing (TDM) in systems that require multi-user access. For example, in some WLAN networks, OFDM is combined with TDM to provide multiple access capabilities. That is, OFDM is used for uplink transmissions from one user at a time, and multi-user access is arranged in a TDM manner. However, this type of uplink access method cannot effectively support cellular network deployment and mobility because it does not provide the quality of service and features required for cellular networks. In addition, these approaches do not support circuit data services such as voice.

According to one aspect, the present invention provides a wireless terminal for communicating over a shared OFDM band, the wireless terminal comprising: a first for generating and transmitting a low rate mode OFDM transmission in a first frequency band of the OFDM band; Transmission chain; And a second transmission chain for generating and transmitting burst mode transmissions in a second frequency band of the OFDM band, wherein the first frequency band is different from the second frequency band.

In some embodiments, the first transmission chain is power controlled and the second transmission chain is rate controlled.

According to another aspect, the present invention provides a wireless terminal for communicating over a shared OFDM band, the wireless terminal comprising: a first transmission for generating and transmitting a low rate mode OFDM transmission in a first frequency band of the OFDM band And a first transmission chain that causes the first frequency band to hop around at frequencies within the subset of the shared OFDM band allocated for low rate mode OFDM transmission. Include.

In some embodiments, the first transmission chain comprises a space time encoder configured to perform space time encoding to generate a signal to be transmitted during each OFDM transmission interval as the low rate mode OFDM transmission.

In some embodiments, the wireless terminal comprises a plurality of N transmit antennas, where N is two or more, and the first transmission chain is adapted for each set of N OFDM transmission intervals as the low rate mode OFDM transmission. And a space-time encoder configured to perform space-time encoding to generate each STC subblock comprising symbols for M subcarriers per N transmission intervals to be transmitted on the transmit antenna.

In some embodiments, the first transmission chain comprises a hopping pattern generator that causes the first frequency band to hopping at a frequency within a subset of the shared OFDM band allocated for low rate mode OFDM transmission, the hopping pattern Generates hops with a hopping unit equal to the size of the STC blocks.

In some embodiments, each STC subblock further includes pilot symbols.

In some embodiments, each STC subblock further includes N pilot symbols on each single subcarrier at each end of that STC subblock.

In some embodiments, the first transmission chain comprises: at least one low rate signal source; For each low rate signal source, at least one configured to generate each spreading sequence for each symbol by multiplying each symbol of the low rate signal source with each orthogonal spreading function from the set of orthogonal spreading functions. Distinct orthogonal diffusion function; And a combiner for summing the spreading sequences in time to produce a synthesized sequence to be transmitted using the first frequency band.

In some embodiments, the wireless terminal comprises a plurality of N transmit antennas, where N is two or more, and the first transmission chain is each during each set of N OFDM transmission intervals as the low rate mode OFDM transmission. A space-time encoder configured to perform space-time encoding to generate each STC subblock that includes M symbols for subcarriers per N transmission intervals to be transmitted on a transmit antenna of the synthesized sequence; It is input to the encoder.

In some embodiments, the set of orthogonal spreading functions include Walsh codes.

In some embodiments, the at least one low rate signal source comprises: a DL (downlink) channel condition (CQI / CLI) feedback channel; A DL ACK / NAK signaling channel; An uplink (UL) buffer status channel; An UL transmit power margin channel; An UL rate indicator channel; At least one of a UL fixed data rate dedicated traffic channel.

In some embodiments, the wireless terminal is further configured to apply a variable number of Walsh code channels to the at least one low rate signal source depending on the required data rate and / or the need for protection.

In some embodiments, the wireless terminal comprises a control channel receiver for receiving power control commands in connection with the low rate mode OFDM transmissions; And a power control function configured to apply transmit power adjustment to the low rate mode OFDM transmissions in accordance with the power control commands.

In some embodiments, the wireless terminal transmits an initial access attempt on an uplink access channel; A power control function configured to determine a long term estimated downlink power measurement of a signal received over a downlink channel and initially transmit the low rate mode OFDM transmission at a transmit power determined according to the estimated downlink power measurement and; And a control channel receiver for receiving power control commands for increasing / unchanging / decreasing transmission power of the low rate mode OFDM transmission after the initial access attempt.

In some embodiments, the wireless terminal further comprises a control channel receiver for receiving channel assignment information that enables identification of at which frequency and at which time to transmit the low rate mode OFDM transmissions.

In some embodiments, the wireless terminal further comprises a control channel receiver for receiving channel assignment information enabling identification of at which frequency and at which time to transmit the low rate mode OFDM transmissions, the channel assignment The information includes a hopping pattern identifier that enables the wireless terminal to perform hopping according to one of a set of orthogonal hopping patterns.

In some embodiments, the wireless terminal further includes a cover code generator configured to apply a cell specific cover code to generate all low rate mode OFDM transmissions.

In some embodiments, the wireless terminal further includes at least one channel coder configured to apply channel coding to low rate signal sources prior to forming the STC blocks.

In some embodiments, the channel coders have a block size that covers several hoppings to achieve diversity gain and intercell interference averaging.

In some embodiments, the STC block size is N × M plus pilot carriers, where M is a number such that the block size is less than a coherence bandwidth. .

In some embodiments, the wireless terminal further comprises an access channel transmission chain configured to generate an OFDM access signal occupying a randomly selected slot selected from a plurality of slots comprising a frame, wherein each slot is in a given block. Include OFDM time-frequency.

In some embodiments, the wireless terminal further comprises a control channel receiver for receiving an identifier of a plurality of signature definitions for use in a coverage area, the wireless terminal randomly selecting one of the plurality of signatures and The signature is applied to generate the access attempt.

In some embodiments, each slot includes four OFDM symbols and there are sixteen different possible signatures.

In some embodiments, the wireless terminal is further configured to map the signature onto OFDM carriers based on a Peano-Hilbert plane filling curve.

In some embodiments, the access channel is overlaid on low rate mode OFDM transmissions of other wireless terminals.

In some embodiments, the wireless terminal is configured to function in an active and standby state, further comprising a control channel receiver for receiving a system access channel assignment when entering the standby state; System access channel assignment is associated with specific subcarriers and OFDM symbols to be used as a system access channel, and the wireless terminal is further configured to use the system access channel to transmit pilot and system access requests while in the standby state. do.

In some embodiments, the system access channel includes two or more subcarriers allocated during certain particular OFDM symbols.

In some embodiments, the system access channel is used to transmit differentially encoded access requests including at least one state indicating a need for low rate mode and / or burst mode capacity to be scheduled.

In some embodiments, the wireless terminal further includes a second transmission chain for generating and transmitting burst mode OFDM transmission transmissions occupying the allocated space in OFDM frequency-time.

In some embodiments, the second transmission chain comprises a space-time encoder configured to perform space-time encoding to generate a signal to be transmitted during a plurality of OFDM transmission intervals as the burst mode OFDM transmission.

In some embodiments, the wireless terminal includes a plurality of N transmit antennas, where N is two or more, and the second transmission chain is configured for each of a plurality of assigned STC subblock transmission frequency-time locations. A space-time encoder configured to perform space-time encoding to generate each STC subblock to be transmitted on the transmit antenna.

In some embodiments, each STC subblock further includes pilot symbols.

In some embodiments, each STC subblock further includes N pilot symbols on each single OFDM subcarrier at each end of that STC subblock.

In some embodiments, the wireless terminal further comprises a control channel receiver for receiving a downlink signaling channel comprising instructions for burst mode transmission.

In some embodiments, the instructions include a definition of a coding / modulation primitive and the assigned STC subblock transmission frequency-time space.

In some embodiments, the instructions further include rate control commands, wherein the wireless terminal is configured to change the coding / modulation primitive in accordance with the rate control commands.

In some embodiments, the wireless terminal measures long term power strength from a serving transmitter and sets up coding / modulation using multi-level progressive coding and modulation feed forward transmission. It is further configured to.

In some embodiments, the second transmission chain is configured to cause the assigned STC subblock transmission frequency-time positions to hop around at a frequency within a subset of the shared OFDM band to which burst mode traffic has been allocated. A hopping pattern generator defining subblock transmission frequency-time locations.

In some embodiments, the wireless terminal further comprises an access channel transmission chain configured to generate an OFDM access signal occupying a randomly selected slot selected from a plurality of slots comprising a frame, wherein each slot is in a given block. Include OFDM time-frequency.

In some embodiments, the wireless terminal is configured to function in an active and standby state, further comprising a control channel receiver for receiving a system access channel assignment when entering the standby state, wherein the system access channel assignment is a system; Associated with specific subcarriers and OFDM symbols to be used as an access channel, the wireless terminal is further configured to use the system access channel to transmit pilot and system access requests while in the standby state.

According to another aspect, the present invention provides a wireless terminal for communicating over a shared OFDM band, which wireless terminal generates an OFDM access signal occupying a randomly selected slot selected from a plurality of slots comprising a frame. A configured access channel transmission chain, each slot containing an OFDM time-frequency of a given block.

In some embodiments, the wireless terminal further comprises a control channel receiver for receiving an identifier of a plurality of signature definitions for use in a coverage area, the wireless terminal randomly selecting one of the plurality of signatures and The signature is applied to generate the access attempt.

In some embodiments, each slot includes four OFDM symbols and there are sixteen different possible signatures.

In some embodiments, the wireless terminal is further configured to map the signature onto OFDM carriers based on a Peano-Hilbert plane filling curve.

In some embodiments, the access channel is overlaid on low rate mode OFDM transmissions of other wireless terminals.

In some embodiments, the wireless terminal is configured to function in an active and standby state, further comprising a control channel receiver for receiving a system access channel assignment when entering the standby state, wherein the system access channel assignment is a system; Associated with specific subcarriers and OFDM symbols to be used as an access channel, the wireless terminal is further configured to use the system access channel to transmit pilot and system access requests while in the standby state.

In some embodiments, the system access channel includes two or more subcarriers allocated during certain particular OFDM symbols.

In some embodiments, the system access channel is used to transmit differently encoded access requests including at least one state indicating a need for low rate mode and / or burst mode capacity to be scheduled.

In some embodiments, the wireless terminal further includes a second transmission chain for generating and transmitting a burst mode OFDM transmission occupying the allocated space in OFDM frequency-time.

In some embodiments, the second transmission chain comprises a space-time encoder configured to perform space-time encoding to generate a signal to be transmitted during a plurality of OFDM transmission intervals as the burst mode OFDM transmission.

In some embodiments, the wireless terminal includes a plurality of N transmit antennas, where N is two or more, and the second transmission chain is configured for each of a plurality of assigned STC subblock transmission frequency-time locations. A space-time encoder configured to perform space-time encoding to generate each STC subblock to be transmitted on the transmit antenna.

In some embodiments, each STC subblock further includes pilot symbols.

In some embodiments, each STC subblock further includes N pilot symbols on each single OFDM subcarrier at each end of that STC subblock.

In some embodiments, the wireless terminal further comprises a control channel receiver for receiving a downlink signaling channel comprising instructions for burst mode transmission.

In some embodiments, the instructions include a coding / modulation primitive and definition of the assigned STC subblock transmission frequency-time positions.

In some embodiments, the instructions further include rate control commands, wherein the wireless terminal is configured to change the coding / modulation primitive in accordance with the rate control commands.

In some embodiments, the wireless terminal is further configured to measure long term power strength from the serving base station and set up coding / modulation using multilevel gradual coding and modulation feedforward transmission.

In some embodiments, the second transmission chain is configured to cause the assigned STC subblock transmission frequency-time positions to hop around at a frequency within a subset of the shared OFDM band to which burst mode traffic has been allocated. A hopping pattern generator defining subblock transmission frequency-time locations.

According to another aspect, the present invention provides a network terminal for receiving communications on a shared OFDM band, the network terminal receiving burst mode OFDM transmissions on the first subset of the shared OFDM band and sharing the shared signal. And a receiver for receiving low rate mode OFDM transmissions on the second subset of OFDM bands.

In some embodiments, the network terminal is further configured to extract burst mode OFDM transmissions of the plurality of wireless terminals from the first subset and extract low rate mode OFDM transmissions of the plurality of wireless terminals from the second subset. .

In some embodiments, the network terminal further includes a control channel output for controlling the frequency-time locations at which the wireless terminals are intended to transmit their low rate mode transmissions.

In some embodiments, the control channel identifies each orthogonal hopping pattern for low rate mode OFDM transmission to each wireless terminal.

In some embodiments, the network terminal determines the quality of low rate mode OFDM transmissions for each wireless terminal transmitting low rate mode OFDM transmissions and for the wireless terminal transmitting each low rate mode OFDM transmissions. And a power control function configured to generate power control signals in connection with rate mode OFDM transmissions.

In some embodiments, the network terminal is further configured to assign each system access channel for each standby wireless terminal and to transmit an identifier of each system access channel via a control channel, wherein the network terminal is And are configured to monitor the system access channels to confirm capacity requirements from the wireless terminals in the standby state.

In some embodiments, the network terminal is further configured to maintain timing and synchronization using the system access channels for the idle wireless terminals.

In some embodiments, the capacity requirements can be requests for burst mode or low rate mode capacity.

In some embodiments, the network terminal further includes a control channel output for controlling which wireless terminals will transmit burst mode OFDM transmissions.

In some embodiments, the control channel output identifies at which frequency each wireless terminal will transmit a burst mode OFDM transmission and at what time the burst mode OFDM transmission will be transmitted.

In some embodiments, the network terminal is further configured to perform adaptive rate control for the burst mode transmission.

In some embodiments, the network terminal is configured to monitor a random access channel, wherein the random access channel includes a plurality of slots, each slot includes a plurality of OFDM symbol intervals, and a plurality of Ms in each slot. M access attempts may be received during one slot including the two signatures, which are overlaid on transmissions of the active wireless terminals.

In some embodiments, the network terminal is further configured to transmit an identifier of the signatures for use on the random access channel.

In some embodiments, the network terminal is further configured to grant system access based on the detected access attempts on the random access channel.

According to yet another aspect, the present invention includes a plurality of wireless terminals in which respective Walsh codes are assigned to each wireless terminal, wherein each user data element generated by the wireless terminal comprises a plurality of OFDM symbols. In addition to being transmitted on each subcarrier spread in time across the terminals, multiple wireless terminals provide a system for transmitting each data element simultaneously on the same subcarrier.

According to another aspect, the invention comprises a plurality of wireless terminals assigned at least one Walsh code for each channel of the wireless terminal for a given wireless terminal, wherein each user data element of any wireless terminal is plural. A plurality of wireless terminals provide a system for transmitting simultaneously on the same OFDM symbol subband, while being transmitted on an OFDM symbol subband spread frequencywise over the OFDM subcarriers of.

According to another aspect, the present invention provides a method of communicating over a shared OFDM band, comprising: generating and transmitting a low rate mode OFDM transmission in a first frequency band of the OFDM band; Generating and transmitting a burst mode transmission in a second frequency band of the OFDM band, wherein the first frequency band provides a different method than the second frequency band.

In some embodiments, the method further comprises: receiving power control commands and controlling transmit power of the low rate mode OFDM transmission in accordance with the power control commands; Receiving rate control commands and controlling a transmission rate of the burst mode OFDM transmission in accordance with the rate control commands.

Other aspects of the present invention provide respective methods configured to implement a transmit / receive / control method executed by any of the above summarized wireless terminals or base stations.

Other aspects of the present invention provide respective systems comprising a series of any of the above summarized base stations in combination with a series of any of the above summarized wireless terminals.

Other aspects of the present invention provide a respective computer readable medium having stored thereon instructions for executing a transmission / reception / control method executed by any of the above summarized wireless terminals or base stations.

Other aspects and features of the invention will be apparent to those skilled in the art upon reviewing the following description of specific embodiments of the invention.

The present invention will now be described in more detail with reference to the accompanying drawings.
1 is a system diagram of an OFDMA system provided by one embodiment of the present invention.
2 shows an example of time-frequency resource allocation in a common wireless channel according to an embodiment of the present invention.
3 is a block diagram of a transmission signal chain that may be used to generate a mode-1 uplink signal in accordance with an embodiment of the present invention.
4 is an example of a time-frequency plot for mode-1 transmissions of a single user.
5 is an example of a time-frequency plot for mode-1 transmissions of multiple users.
6A and 6B are another example of a time-frequency plot for mode-1 transmissions of multiple users.
7 is an example where spreading is performed in the frequency dimension while mode-1 transmissions of multiple users are separated using orthogonal Walsh codes rather than STC subblocks.
8 is an example in which spreading is performed in the time dimension while mode-1 transmissions of multiple users are separated using orthogonal Walsh codes rather than STC subblocks.
9 is an example of how RACH slots are defined in accordance with an embodiment of the present invention.
10A is a block diagram of a transmitter showing both RACH and mode-1 channels combined in a mode-1 frequency space.
FIG. 10B is another example of a transmitter design similar to the transmitter design of FIG. 10A but in which encoding across subblocks is used.
11 is a flowchart for a method of joint RACH detection and uplink synchronization.
12 is an example of a time-frequency diagram illustrating the allocation of OFDM subcarriers for an example of mode-2 operation.
13 is a block diagram of an example transmitter for mode-2 operation.
14 is a flowchart of an example method of uplink rate control.
15A is a block diagram of an example of how mode-1 and mode-2 signals are combined.
15B shows an example in frequency-time for how the Mode-1 and Mode-2 signals are combined.

Methods and apparatus are provided for uplink multi-user access to reduce multiple access interference such that spectral efficiency and high data rate limits in a common wireless channel are increased. The methods and apparatus disclosed herein are based on Orthogonal Frequency Division Modulation (OFDM) configured to provide an effective uplink multi-user access scheme that can be used in a wireless communication network. Therefore, from here on, the OFDM based uplink multi-user access provided by the present invention will be referred to simply as Orthogonal Frequency Division Multiple-Access (OFDMA).

A full uplink operation design is provided, including:

Uplink setup;

Multiple access scheme;

Definition of uplink channels;

Pilot structure;

Synchronization strategy;

Coding modulation scheme; And

OFDMA resource allocation strategy.

It is anticipated that embodiments of the invention may be implemented that feature any subcombination from one or more of the elements introduced above to all of the elements.

OFDMA Basic concepts

Referring now to FIG. 2, an example of time-frequency resource allocation made in accordance with the OFDMA scheme provided by one embodiment of the present invention is shown.

The modulation technique used in OFDMA is OFDM. OFDM is a digital modulation method in which a data set is mapped to a set of OFDM subcarriers. Each circle in FIG. 2 (one of which 99 is identified as an example) represents transmission of a single subcarrier during a single OFDM symbol transmission period. Thus, the horizontal axis in FIG. 2 represents frequency, the vertical axis represents time, and time increases to the bottom of the page. In the example shown, the OFDM band is shown to include 32 subcarriers. It will be appreciated that this is only an example and any suitable number of subcarriers may be used. The number can be quite large, such as 1024. However, this is a simplified diagram in that the actual frequency response associated with each of the subcarriers substantially overlaps. However, in OFDM, the frequency response of each subcarrier is designed to be orthogonal to the frequency response of each other subcarrier so that the data modulated to each subcarrier is independently recovered at the receiver.

Note that in conventional OFDM, an OFDM symbol is defined as consisting of simultaneous transmission on the entire set of orthogonal subcarriers defining an OFDM channel. The OFDM symbol is transmitted from a single source to the destination.

According to the OFDMA scheme provided by an embodiment of the present invention, the common radio channel 50 is implemented using the OFDM transmission scheme within the entire OFDM band. However, rather than dedicated allocation of the entire OFDM band to a single transmitter, for a given symbol period, two OFDM bands can be used interchangeably to provide two different OFDMA modes provided by embodiments of the present invention. It is divided into frequency bands 51 and 53. These two different OFDMA modes are generally referred to herein as mode-1 and mode-2, respectively. In the figure legend, subcarriers used for mode-1 are generally labeled 60 and subcarriers used for mode-2 are generally labeled 62. The first frequency band 51 has the first sixteen subcarriers of the OFDM band 50 and the second frequency band 53 has the second sixteen subcarriers of the OFDM band 50. Details of Mode-1 and Mode-2 will be further described below individually. Mode-1 is preferably used to provide low rate circuit-oriented connectivity to multiple users simultaneously using orthogonal code separation, while mode-2 provides higher rate bursty packet connectivity. Used to

2 shows an example of time-frequency resource allocation for Mode-1 and Mode-2, which change over time. During symbol periods t _i to t _{i +9} , the first allocation is shown with a first frequency band 51 assigned to mode-2 traffic and a second frequency band 53 assigned to mode-1 traffic. During symbol periods t _{i +10} and t _{i +11} , the entire OFDM band 50 is dedicated to mode-1 traffic. Finally, after the symbol period t _{i +12} , the first frequency band 51 is assigned to mode-1 traffic and the second frequency band 53 is assigned to mode-2 traffic. Note that the size of the first and second bands 51, 53 does not change with time only because the frequency bands in this example are equal to each other. For example, if 10 subcarriers are assigned to mode-1 traffic and 22 subcarriers are assigned to mode-2 traffic, the frequency between the two bands when switching between mode-1 and mode-2 traffic occurs The boundary point 55 of will move.

In the example shown, the division of OFDM band 50 between frequency bands 51 and 53 is equal to 16 subcarriers per band. In one embodiment, the time-frequency resource allocation 100 shown by the example in FIG. 2 for Mode-1 and Mode-2 may be the same across the wireless network, and the same allocation occurs in multiple cells. . In another embodiment, the time-frequency resource allocation (provided for Mode-1 and Mode-2) may vary from cell to cell and from time to time. For example, a network administrator or individual base station can dynamically reconfigure resource allocation. That is, the respective bandwidths allocated to mode-1 and mode-2 are not limited to the same. In some embodiments, dividing the OFDM band 50 into frequency bands 51, 53 is static. In another embodiment, dividing the OFDM band 50 between the frequency bands 51, 53 is based on traffic load balancing between mode-1 and mode-2 in the cell of the wireless network. Moreover, while only two frequency bands are shown in the illustrated example, it is noted that there may be further division of frequency bands to define multiple channels for both mode-1 and mode-2 traffic. Subbands of mode-1 and mode-2 assigned bands are used for simultaneous transmission by different users.

Frequency hopping of mode-1 and mode-2 within the OFDM band helps to combat deep fades in both time and frequency dimensions, and also based on traffic load and overall traffic conditions. It is intended to allow additional adaptive channel resource allocation of mode-1 and mode-2.

Moreover, frequency hopping in mode-1 and mode-2 reduces the need for the same mode-1 and mode-2 splitting over a wireless network and over time within a single cell. As a result, either mode-1 or mode-2 may prevail in different areas of the wireless network as determined by the UE traffic distribution (ie, more bandwidth may be allocated). In fact, one or both of the two OFDMA modes, Mode-1 and Mode-2, may not be present in all areas of the wireless network at a given moment. However, Mode-1 preferably always exists in the wireless network because Mode-1 more readily supports the low rate signaling channels used to maintain wireless network operation.

For both mode-1 and mode-2 operation, for a given symbol period, simultaneous (but not necessarily synchronized) from different UEs based on the mode of operation of each particular UE during that period and the mapping pattern for that period. Need not be) transmissions are mapped to one or both of the frequency bands 51, 53.

Once a frequency band and mode of operation is assigned to a given user, many different methods for actually mapping the data to the band can be used. In an embodiment of the invention, the mapping pattern defines each set of space-time coded sub-blocks (STC-SB) in the time-frequency dimension. STC-SB is the mapping of data to a wireless channel with both time and frequency dimensions. That is, a single STC-SB spans multiple subcarriers and multiple symbol periods.

An example of a single STC-SB 80 is shown in FIG. The STC-SB includes a limited number of contiguous OFDM subcarriers in the frequency dimension (10 in the illustrated example) and one or more OFDM symbol periods (two in the illustrated example) in the time dimension.

To support coherent detection, pilot symbols are included in the STC-SBs. For example, the STC-SB 80 has two pilot symbols 82 at each end of its frequency dimension and allows interpolation in frequency across the bandwidth between these pilot symbols. The remaining subcarriers are used for data. The maximum size of the STC-SB is typically limited by the frequency coherence bandwidth. Interpolation between pilots separated more than coherence bandwidth will not yield an effective channel estimate. This enables receivers to use simple channel estimation methods.

It should be noted that the frequency coherence bandwidth is typically smaller than the corresponding bandwidths of the frequency bands 51 and 53. Thus each frequency band 51 and 53 can be advantageously further sub-divide so that a plurality of STC-SBs can be transmitted simultaneously in each frequency band 51 and 53 without overlapping in the frequency domain. have. Thus, in some embodiments, the STC subblock may be considered the minimum uplink transmission unit provided by OFDMA. STC-SB may also be used as a time-frequency hopping unit. OFDMA is quite easily applied to multi-user access because there is no constraint to force all STC-SBs transmitted at the same time to belong to the same UE. In the following description, it is assumed that the STC subblock is the minimum uplink transmission unit for both mode-1 and mode-2 operation. However, it will be appreciated that once the respective bands are defined, other data mapping methods for mode-1 and mode-2 may be used.

In order to support uplink transmit power measurement, in some embodiments pilots from each UE are generated from a coded sequence and power boosted. The pilot symbol positions of the users in the cell are preferably offset from each other in the frequency direction or in the time direction. This pilot channel implementation does not require a preamble.

Within frequency band 50 of FIG. 2, mapping is done such that STC-SBs from different UEs do not overlap in time or frequency within the same cell / sector for both mode-1 and mode-2 operation. All. This has the effect of significantly reducing intracellular interference. Moreover, in some embodiments, orthogonal mapping patterns are also used for each user that also provide time-frequency diversity. Further discussion below is provided below regarding orthogonal hopping (mapping) patterns that may be used for mode-1 or mode-2 transmissions in connection with the detailed description of mode-1. Orthogonal hopping patterns that reduce both intra-cell and inter-cell interference are described.

Cell specific covering code

In some embodiments, cell specific covering code is applied to transmissions from all UEs in a particular cell before STC-SB mapping (hopping) is performed. If cell specific spreading codes are used across the entire wireless network, the result is that the same set of Walsh codes can be used for every cell. As noted above, orthogonal hopping (mapping) patterns are also used for this purpose and will be discussed further below.

Advantages of frequency-domain spreading are multi-user detection in the frequency domain, which significantly increases interference mitigation and / or performance of an optimal / sub-optimum maximum a posteriori probability (MAP) receiver in the frequency domain. .

MIMO  action mode

OFDMA using various user configurations may be used. The simplest embodiment is that each UE has one antenna and each base station has one antenna (one antenna per sector if sectored). In another embodiment, a SIMO (single input, multiple output) scheme with a single transmit antenna and multiple receive antennas is used. In yet another embodiment, a MIMO (multiple input, multiple output) scheme is used that features multiple transmit antennas and multiple receive antennas. In another embodiment, a MISO (multiple input, single output) configuration is used. In another embodiment, the antenna configuration used for mode-1 and mode-2 transmissions are different. For example, to save power, the UE applies SIMO for mode-1 and MIMO for mode-2.

To support two antenna MIMO transmission, the STC-SB must include at least two OFDM consecutive symbols in the time domain. More generally, in N × M systems, there must be at least N OFDM consecutive symbols in the STC-SB. The number of consecutive OFDM subcarriers in the STC-SB may again be determined by the frequency coherence bandwidth of the common wireless channel.

send mode

As pointed out above, uplink transmission is classified into two modes. Mode-1 supports the provision of user dedicated channels with a fixed data rate to support real time service, uplink signaling and simple messaging. Mode-2 supports the transmission of high speed data bursts. The partitioning of time-frequency resources between these two modes is preferably based on traffic load balancing between the two modes in the wireless network.

mode -1 description

As discussed above, mode-1 operation occurs within the frequency band of the entire OFDM band. The description below is for operation of the mode-1 band when the mode-1 band is assigned at a given moment. As noted above, this band may be assigned a fixed or variable size, either statically or dynamically.

Mode-1 according to one embodiment of the present invention is designed to support several simultaneous transmitted (parallel) transmission channels per user. One or more of these concurrently transmitted parallel transport channels may be allocated per active UE according to bandwidth requirements. These transport channels may have corresponding data rates to support real time service (such as voice), uplink signaling and simple messaging. In some embodiments, corresponding data rates are maintained by using power control and adaptive modulation.

More specifically, Mode-1 operates in an open or closed power control loop to provide parallel transmission channels per UE carrying fixed rate circuit data, low delay circuit data or high speed packet data.

On a per UE basis, mode-1 signals include one or more orthogonal spreading codes used to separate transport channels belonging to a single UE. Thus, the modulation scheme for mode-1 may be referred to as "multicode (MC) -OFDMA". Since a single UE can transmit code separated transport channels synchronously, the orthogonality of the code separated transport channels is guaranteed over the wireless channel.

Multicode-OFDMA (MC-OFDMA) introduces code multiplexing on top of the "frequency and time division" generated by OFDMA.

The multiple parallel transport channels may be signaling channels needed for network maintenance or may be voice channels requiring real time service. Examples of various signaling channels that may be included in the uplink are further provided below.

Referring to FIG. 3, there is shown a schematic diagram of a transmit signal chain 200 that can be used to generate a mode-1 uplink signal for a single UE. It will be appreciated that the transmit signal chain 200 may be implemented using a combination of properly configured hardware, software and firmware.

The transmit signal chain 200 includes a number of parallel transport channels TC ₁ 100, TC ₂ 200,..., TC _N 110. The number of channels is specified by system design and bandwidth considerations. At a minimum, a user who wants to operate in mode-1 will need at least one such transport channel. Each transport channel TC ₁ (100), TC ₂ (200), ..., TC _N (110) is coupled in series to each orthogonal code spreading function (120, 122, ..., 130). The output of each of the spreading functions 120, 122,... 130 is coupled to an adder 35 that sums the so spread sequences. The output of adder 35 is coupled to pilot and space-time (ST) encoder 30, which provides two parallel outputs to hopping pattern generators (HPG) 31 and 32, respectively. do. The hopping patterns are the same for the two antennas. HPGs 31 and 32 are respectively coupled to IFFT (fast Fourier inverse transform) functions 33 and 34, which have outputs connected to corresponding antennas 21 and 22. . In embodiments without hopping, HPGs 31 and 32 will be omitted.

In operation, each transport channel 100, 102, ..., 110 delivers the modulated data symbols to each orthogonal code spreading function 120, 122, ..., 130 one at a time. For example, as shown in FIG. 3 at a given moment, the transmission channels 100, 102, ..., 110 correspond to respective symbols S ₁ , S ₂ ,..., S _N. It is shown to provide to the orthogonal code spreading functions 120, 122, ..., 130. The modulation technique used to modulate each modulated data symbol can be, for example, QAM, 16 QAM or 64 QAM. Moreover, the transmission channels do not have to use the same symbol modulation technique.

Each orthogonal spreading function 120, 122, ..., 130 multiplies each symbol received from the transmission channel with multiple chips of each orthogonal code. In a preferred embodiment, these orthogonal codes are Walsh codes of length L = 16 so that each transport channel produces 16 chips after spreading. It will be appreciated that other sizes of Walsh codes, and other types of orthogonal codes may be used.

Corresponding chips from each orthogonal code spreader are summed using adder 35. The output of adder 35 is a sequence of L chips, each chip containing information for each transmission channel. The output of adder 35 is provided to pilot and ST (space-time) -encoder 30. In embodiments with multiple transmit antennas, pilot and ST encoder 30 have two roles. First, in two antenna systems (or N antenna systems) it processes a sequence of chips, one for transmission on each antenna for two (N) symbol periods, two (N) Generate chips of the sequence of. In one embodiment, this process is STBC. Of course, other mechanisms for generating two (N) sequences may be used. For example, S.M. Alamouti's "A Simple Transmit Diversity Technique for Wireless Comminications" (IEEE J. Select. Areas Commun., Vol. 16, No. 8, pages 1451-1458, October 1998), and V. Tarokh, H. Jafarkhani, And AR See Calderbank's "Space-time Block Codes from Orthogonal Designs" (IEEE Trans. Inform. Theory, July 1999). For example, a sixteen chip signal may be processed by a space-time encoder to generate two 8 × 2 STC subblocks, one for each antenna. Another function is to generate and add UE specific pilot symbols to both sides of the STC-SB generated from the L synthesis chips. This results in a 10 × 2 block for each antenna having pilot symbols 140 and STC symbols 142 and generally illustrated at 16. For each antenna it is delivered to each HPG 31, 32. The HPGs 31 and 32 determine which subband of the mode-1 FFT bandwidth will be used for that particular transmission, and the IFFT functions 33 and 34 perform frequency to time conversion.

At any given moment the HPGs 31 and 32 map the STC-SBs they have received to the subbands of the mode-1 OFDM band currently being used for mode-1 transmission. In mode-1 transmission, hopping patterns are unique to a single UE in a cell / sector and may be pseudo-random. Each user's mapping is preferably spread across the time-frequency dimension using a random hopping pattern to achieve time-frequency diversity. The hopping unit is preferably an STC subblock. Hopping patterns are discussed in more detail below.

An optimized MC-OFDMA user mapping design is provided for both fast mobility and nomadic deployment scenarios. Subband mapping is specified by channel propagation characteristics.

4 provides an example of transmission in time and frequency of a user's mode-1 signal. Again, the horizontal axis represents frequency and the vertical axis represents time. In this example, the mode-1 frequency band is divided into three subbands, each of which is sized to carry an STC subblock in the form of subblock 16 of FIG. The mode-1 band also includes SACH subcarriers 131, 133 in this example. These are further described below. During each symbol period, the user can see that in one of these three subbands, the subbands used hop around. Thus, during the shown symbol periods t ₁ ,..., T ₉ , the user sequentially orders the STC subblock in each of the subbands 130, 134, 132, 130, 134, 132, 130, 134, 132. Send.

Each of the subbands defines a channel for mode-1 transmission. Preferably, two users in a sector are not assigned the same channel at the same time. Thus, in the example of FIG. 4, at time and frequency locations not occupied by the user's mode-1 transmission, other user's mode-1 transmissions are transmitted. In this way, users are separated at frequencies within the cell. In another embodiment, if very good synchronization can be achieved between users, overlapping bands may be assigned to users as long as users use different orthogonal spreading codes.

Such MC-OFDMA based Mode-1 links may support high speed packet data services as well as low delay and fixed data rate circuit data such as voice, simple messages and signaling. In the simulation, MC-OFDMA was found to have 5-10 times the spectral efficiency than 3G wireless systems using CDMA. In addition, the simulated MC-OFDMA system has also been found to provide an order of magnitude increase over 3G wireless systems using CDMA, respectively, in system capacity and uplink data rate. These results do not mean that not all implementations will be so effective.

The transport channels of FIG. 3 preferably comprise channel coding (not shown). Channel coding block spans preferably cover several hoppings for a user to achieve diversity gain and intercell interference averaging.

5 is another example of how the mode-1 band may be occupied. This example shows time on the vertical axis and STC subblocks on the horizontal axis. The STC subblocks assigned to User 1 are generally denoted as 182, denoted as 183 for User 2, and as 184 for User 3. In this case, these three users are assigned the same transmission rate R, so the distribution of STC subblocks for these three users allocates the same number of subblocks per user. Note that certain hopping patterns have been created using synchronous quadratic congruence codes described below.

In an MC-OFDMA system, code division is used for simultaneous transmission of data of a single UE in the same STC subblock. Because each STC subblock is exclusively assigned to only a single user in a sector, there is no user-to-user interference in each STC subblock, but due to the loss of orthogonality caused by the fading channel, the user internal self interference (intra) -user self-interference) exists. MC-OFDMA can reduce its own interference by appropriately using orthogonal spreading codes in the uplink due to the accurate synchronization characteristic of the orthogonal codes, and the MC-OFDMA system is also because all Walsh codes are transmitted through the same propagation channel. This enables low complexity channel estimation and simple linear multicode channel detection.

Adaptive ( Adaptive ) SF MC - CDMA

The spreading factor in each of the transport channels can be variable and is preferably set according to traffic load and channel conditions. After spreading, one symbol is represented by K symbols. This number of K is defined as the "spreading factor". Note that K symbols will take K subcarriers in an OFDM system. Changing the spreading coefficient is realized by changing the mapping of the STC subblock units covered by the spreading code.

Thus, in some embodiments, the spreading factor is controlled by the base station's scheduler in accordance with the traffic load and channel condition for a particular UE. A base station can assign two or more Walsh channels to circuit data channels that require higher protection and higher data rates. In mode-1, the signal is power controlled. That is, the data load that can be carried by each Walsh channel is fixed. Therefore, the more Walsh codes a single user has, the higher the data rate. In addition, the lower the code rate used by a given user, the better the protection will be.

6A and 6B, two further examples of how the mode-1 bandwidth is allocated will now be described. 6A shows how hopping can occur in a system with two users. Here, rate R is assigned to user # 1 which is the first user, and rate 2R is assigned to user # 2 which is the second user. This means that there needs to be twice as many STC subblocks that are assigned to the second user than that assigned to the first user. Subblocks assigned to user # 1 are generally labeled 180 'and subblocks assigned to user # 2 are generally labeled 181'. It can be seen that there are twice as many subblocks assigned to user # 2 than those assigned to user # 1.

In another example shown in FIG. 6B, there are four users, user # 1 is assigned rate R, user # 2 is assigned rate R, user # 3 is assigned rate R / 2, user # 4 is assigned rate R / 2. These subblocks assigned to user # 1 are generally labeled 185, labeled 186 for user # 2, labeled 187 for user # 3, and labeled 188 for user 4. It can be seen that users # 1 and # 2 have twice as many blocks allocated as users # 3 and # 4. While every STC transmission period contains one subblock for each of user # 1 and # 2, only every second STC transmission period contains one subblock for each of user # 3 and # 4 It includes.

Power control Power Controlled ) MC - OFDMA

Mode-1 operation is used for transmission of a slow traffic channel. In some embodiments, the same band is used for the RACH described below. In some embodiments, the slow traffic channel applies open-loop power control MC-OFDMA technology. An example of the power control solution is given below along with a description of the RACH.

System access channel ( SACH )

In some embodiments, a system access channel is provided for use as a quick uplink paging channel to signal a base station for MAC state transition at both the base station and the UE. A UE that accesses the system, i.e., is in a power-on state, does not transmit in either mode-1 or mode-2 in the standby state. Preferably, SACH signaling has two states: active state and not-active state. The SACH signal is transmitted periodically from all inactive UEs to enable the base station to track the UE timing and maintain synchronization during the UE inactivity mode.

In one embodiment, the SACH for a given user is two or more subcarriers allocated during certain particular OFDM symbols. Preferably, one of these subcarriers is encoded as a pilot channel and the other subcarriers contain at least one state that indicates that the user is requesting Mode-1 and / or Mode-2 capacity to be scheduled. differentially) encoded access requests. The SACH channel is assigned only to the idle users. Once the user is active, the SACH is deallocated and becomes available to other users. The base station can monitor all SACH channels, perform scheduling accordingly, and maintain timing and synchronization during standby.

In the example of FIG. 4, two SACH channels 131, 133 are shown. Each SACH 131, 133 occupies a pair of adjacent subcarriers every every fourth OFDM symbol period. The subcarriers allocated for the SACH channel may be in the frequency direction or in the time direction as shown in FIG. 4.

Preferably, as in the example of FIG. 4, SACH subcarriers are allocated so as not to overlap with mode-1 transmissions of any users in the cell. Once a plurality of SACH channels are defined, they can be assigned to UEs in a cell using, for example, a paging channel. If there is no downlink traffic for an active UE and there is no uplink transmission request from that UE for some period of time, then the base station typically turns off the dedicated uplink channel for that UE and simultaneously attaches the SACH channel to it. Assign. The UE then transitions from an active state to a standby state in accordance with the signaling received from the base station. The UE then notifies the base station using its dedicated SACH if it wishes to initiate uplink transmission. Eventually, the base station will notify the UE to transition from idle to idle state if the UE remains silent for some period of time. Once the user is idle, he or she will have to use the RACH described below to access the uplink system again.

Uplink Signaling  channel

Preferably, a set of parallel low latency circuit data signaling channels for supporting network operation is provided in mode-1 transmission. The definition of these signaling channels is as follows.

1) DL Channel Condition (CQI / CLI) Feedback—Short block coded downlink channel quality indicator and MIMO channel indicator for enabling the base station to perform multi-user scheduling and adaptive coding modulation and MIMO mode adaptation. Preferably, two data rates are defined for this channel: high data rate for fast adaptation and low data rate for slow adaptation.

2) DL ACK / NAK Signaling-Spread signaling to indicate acknowledgment of successful / failed reception of a downlink packet.

3) Uplink buffer status (buffer full)-Short block coded indicator for UE uplink data buffering condition to allow the base station to schedule uplink mode-2 data bursts. Further details on mode-2 are provided below.

4) Uplink Transmit Power Margin-Short block coded indicator for the UE uplink transmit power head room to allow the base station to schedule uplink mode-2 data bursts.

5) Uplink Rate Indicator-Short block coded indicator for Mode-1 and Mode-2 traffic data channel rate indication for base station receiver demodulation and decoding. In mode-1, this rate indication can be used to support UE autonomous scheduling. In mode-2, this channel can also be used to indicate UE MAC identification.

Uplink traffic  channel

As pointed out above, two types of uplink traffic channels are defined as follows.

Fixed Data Rate Dedicated Traffic Channel (Mode-1)

This mode-1 type channel is designed for user-only channels with a fixed data rate to support real-time services, typically voice. This channel is power controlled, preferably open loop power control is applied to support basic operation, and optionally closed loop power control may be applied.

Non-overlapping allocation of STC subblocks among multiple uplink users may avoid intra-user cell interference. It is more desirable to design an orthogonal hopping pattern for assigning to different users. For example, the synchronous secondary joint codes y _k = QCS (a, α, β, k, p) may be used as follows.

Such a hopping pattern can be used for control of users in the cell. For intercell users, the following asynchronous secondary joint codes may be used for control of intercell user hopping.

Sporadic assignment of time-frequency units in OFDM helps to reduce the peak-to-average power ratio (PARR).

In mode-1 transmission, it is more preferable to arrange a random hopping pattern in each STC block such that only one / a few STC subblocks are allowed for each user. In this case, only a small fraction of the subband is transmitted for each OFDM symbol for each user, which is an H-infinity based tone injection method to increase UE transmission power efficiency. It is possible to use several PARR abatement techniques such as) or a constellation shaping method.

The hopping pattern of FIG. 6 was generated using this method.

Uplink  Power control

Power control of the mode-1 traffic channel may be open loop power control. In one embodiment, power control is achieved as follows.

1. The UE transmits the RACH (described in detail below) at power inversely proportional to the long-term estimated DL C / I measurements and the RACH signature spreading factor (more generally, the RACH power increases when the estimate decreases).

2. The base station measures the power of the RACH from the UE and sends back a power control command to the UE to increase / invariant / decrease the transmit power-this power control transmission can also be interpreted as an acknowledgment, In the absence of an acknowledgment, another access attempt is made with increased power.

3. The UE starts uplink transmission on a dedicated slow traffic channel with power based on the power of the RACH adjusted based on the power control command.

4. The base station controls the uplink power based on the frame error rate from the particular UE.

The above description assumes that multiple users are separated in mode-1 using subblocks, preferably using sub-block hopping. In another embodiment of the present invention, multiple users may share OFDM subcarriers using code separation if synchronization between the various users in the cell can be achieved to a sufficiently accurate degree. An example of this is shown in FIG. 7, where signals for UE-1 300, UE-2 302, UE-3 304, ..., UE-M 310 are orthogonal codes, respectively. For example, in the illustrated example, it is shown to be spread by Walsh codes, Walsh-1 320, Walsh-2 322, Walsh-3 342, ..., Walsh-M 326. Although a summer is shown in this figure, this is intended to illustrate that these signals are summed over the air interface and added additively at the receiver. In this embodiment, the full mode-1 bandwidth can be shared by all users at the same time, or as in the previous embodiments multiple subchannels can be defined, but each subchannel is assigned to multiple users. Occupied by According to this embodiment, it is easy to see how the bandwidth allocated to them can be varied by assigning individual users more or fewer Walsh codes.

In another embodiment, MC-CDMA in the time direction is a viable solution in a slow-fading environment or in a nomadic deployment scenario. In this arrangement, pilots can be inserted periodically by each user, with the spacing of the pilots being sufficient to perform accurate channel estimation. In this case, true synchronous CDMA uplink can be achieved and inter-user interference can be completely eliminated. An example of this is shown in FIG. 8, where the same users and Walsh code spreading are shown as in FIG. 7. In this case, however, the transmission is sent on adjacent subcarriers for a series of consecutive OFDM symbols. Therefore, the diffusion is performed in the time dimension instead of the frequency dimension as in the case of FIG.

Thus, during RACH transmission, the BTS generates power control commands based on the RACH and these are applied to it when the mode-1 traffic transmission begins. Then during the active mode-1 transmission, power control commands are generated directly from the mode-1 transmission, for example based on FER, and applied to the mode-1 transmissions.

Random access channel ( RACH )

Another embodiment of the present invention provides a particular wireless network with a random access channel (RACH) for new UEs to access the system. It will be appreciated that other access schemes may be used instead of the RACH and / or SACH. If a UE has just turned on or moved from an area of another wireless network to an area covered by a particular wireless network, that UE may be considered new to that particular wireless network. In either case, for a particular wireless network, a new UE must access that wireless network through a base station.

With reference to FIG. 9, this embodiment of the present invention provides a RACH that is overlaid on top of the entire common radio channel 50 or overlaid only on one of the two bands 51 and 53 shown in FIG. 2. "Overlaid" here means that the RACH is transmitted simultaneously in both time and frequency as well as the transmission of other Mode-1 signals by other users. Thus, RACH is a form of interference for other users.

The RACH is preferably implemented using a long spreading code and then mapped to OFDM symbols in the defined RACH slot. The RACH slot is defined as a set of OFDM symbol periods in time and is preferably continuous. In the example of FIG. 9, each RACH slot consists of four OFDM symbol periods, and four RACH slots, that is, RACH slot-1, RACH slot-2, RACH slot-3 and RACH slot-4 are shown. have.

The RACH channel structure is preferably based on PN spreading, overlaid on MC-OFDMA. For each RACH slot, a plurality of quasi-orthogonal PN codes define a set of RACH signatures. This enables the definition of a set of parallel orthogonal ALOHA channels during each slot. Because of the fact that non-coherent detection is used for the RACH channel, and UE peak power limitation, the spreading coefficient should preferably be very large to support wider coverage. For example, it should be in the range of 2 ¹⁰ to 2 ¹⁴ diffusions. By such processing gain, the power of the RACH signature is transmitted at a very low relative power level, for example -16 dB, which constitutes very weak interference for traffic and signaling channels.

In some embodiments, the accessing UE transmits on the RACH channel as described above. In addition, a power ramping procedure is preferably applied, so that the RACH channel is transmitted with minimal power to reduce interchannel interference for mode-1 traffic and signaling channels. More specifically, initial attempts are made at very low power. The absence of a power control command from the base station is interpreted as a failed attempt and the next attempt is made with slightly increased power.

The RACH channel is mapped to the following resources.

a) RACH signature specific parallel ALOHA channels;

b) Time-Frequency Dimension RACH Slot-This RACH slot is different from the STC subblock unit.

The number of parallel ALOHA channels allowed may be dynamically set by the network based on the traffic load condition or the number of active users. The accessing UE randomly selects the RACH signature based on the slotted ALOHA protocol. These RACH signatures may also be reused by non-adjacent base stations.

The RACH channel structure in this example consists of RACH slots, each RACH slot consists of four OFDM symbols, and there are 15 RACH slots in a 10 ms frame. For each RACH slot, there are 16 RACH signatures available for configuring 16 concurrent RACH access attempts in one RACH slot. In some embodiments, mapping the RACH signature on the OFDM subcarriers is a Peano-Hilbert plane filling curve to obtain better time-frequency diversity for that RACH signature, as shown in FIG. 9. Based on. Golay sequences can be used as the RACH signature for lower peak-to-average power ratio (PARR).

In order to provide a reliable and flexible random access channel to multiple users, the RACH is preferably overlaid on the mode-1 transmission bandwidth. A dedicated long and complex PN / Golay code set is reserved for the RACH of each base station. The base station may determine the RACH PN / Golay code length of the active state according to the total uplink traffic, which length may be statically defined. The base station may broadcast this information through the DL signaling channel.

10A shows an example of a multiplexing scheme for generating a RACH and a mode-1 traffic channel. The RACH channel 200 is shown spread by Walsh-0 210 and covered by a first long code PN-0 using a multiplexer 220. Also shown are the mode-1 channels spread by Walsh-1, Walsh-2, Walsh-3, and Walsh-4, voice 202, CQI 204, ACK / NAK 206, and data 208, respectively. (Additional and / or different channels may be used). These mode-1 channels are combined using adder 221 and covered by long code PN-1 using multiplexer 222. Adder 224 combines the RACH and mode-1 signals. If only the RACH is used for access, the RACH and mode-1 signals will be mutually exclusive.

The PN covering of the mode-1 traffic channel for one UE may be part of a long PN covering code. The covering PN code for each base station is different from those of neighboring base stations so that interference from these base stations can be averaged and whitened. Since the RACH PN code is much longer than the spreading code for MC-OFDMA, the transmit power of the RACH may be much lower than the transmit power of the slow traffic channel. The RACH should be transmitted with as low power as possible to reduce its impact on the slow traffic channel.

Detection of the RACH channel at the base station may be performed based on, for example, a successive interference cancellation approach. Other methods may be used.

In some embodiments, the RACH is also used for initial timing and synchronization. After randomly selecting one of the RACH signatures, the accessing UE transmits using the entire available access band, which preferably includes all mode-1 subcarriers. The base station finds these access attempts and simultaneously performs timing and synchronization to determine the timing offset for that UE, which informs the user when its OFDM symbol transmission should begin so that the transmissions of all UEs are somewhat common at the base station. It will share the OFDM symbol boundary. Offsets may be different because of different distances from the base station.

A detailed method for joint RACH detection is summarized in the flowchart of FIG. These steps are as follows.

Step 11-1: Transfer the input data from the time domain to the frequency domain by an FFT having FFT window 1 and FFT window 2 separately.

Step 11-2: Recover the bits of mode-1 traffic after decoding.

Step 11-3: Re-encode, reinterleave, and remap the recovered bits.

Step 11-4: Regenerate mode-1 traffic by Walsh respread.

Step 11-5: Add mode-1 channel fading to obtain faded mode-1 traffic (additional phase adjustment is required when window 2 is used).

Step 11-6: Mode-1 traffic interference cancellation (subtract faded Mode-1 traffic recovered from the full frequency domain received signal).

Step 11-7: Extract the received RACH after interference cancellation.

Step 11-8: Correlate the received RACH Y _RACH with all RACH signatures and find the maximum.

Step 11-9: the FFT window synchronization search by obtaining a new _RACH Y Y by multiplying the phase vector corresponding to the _RACH Sikkim moved into the window (sync search window).

Step 11-10: Correlate this new Y _RACH with all RACH signatures and find the maximum.

Step 11-11: Find the final maximum among all local maximums in the synchronous search window.

The output of this process is the RACH signature index and sync position (RACH signature and FFT window position correspond to the final maximum).

Uplink  Of transmission set up

The following steps describe a procedure for a UE to initiate a connection with an access network.

1) After powering on, the UE selects the serving base station in synchronization with the base station to adjust timing and frequency and at the same time, for example, by detecting the downlink preamble.

2) The UE listens to the DL signaling channel to find information identifying the RACH PN codes to be used in the corresponding cell / sector.

3) The UE measures the DL long term C / I.

4) The UE transmits a randomly selected RACH code from the code set of the serving base station over the ALOHA RACH channel. The transmit power is determined in inverse proportion to the DL long term C / I measurement.

5) If the base station successfully detects the RACH code, the base station measures the time offset of the UE and then transmits an initial dedicated uplink access channel grant with the RACH code index as well as the time offset information. The UE then detects such a signature for identifying the access grant via the DL signaling channel.

6) The UE adjusts its timing and sends an uplink traffic load request if desired to initiate its ID, its CQI reporting information, and uplink data transmission, e.g., the parallel low latency circuit data channels described above. It transmits back through one initial dedicated uplink signaling channel.

7) The base station schedules uplink multi-user accesses based on measured uplink channel conditions from the mode-1 pilot, and traffic requirements reported from UEs in different activity states.

8) Coding / modulation primitives and channel resource allocations for different UEs are signaled via the DL signaling channel.

Each time the UE needs a new uplink connection, the UE sends a new access request by accessing the SACH. To improve spectral efficiency, the UE can buffer some short messages within a delay tolerance and then transmit them on its dedicated slow traffic channel using the MC-OFDMA scheme. Alternatively, whenever the UE requires a transition to a new connected and active state, a common uplink link channel in the TDM mode of operation may be used to signal the UEs to perform a state transition.

FIG. 10B is a block diagram of another transmitter embodiment similar to that of FIG. 10A, wherein coding is performed over subblocks. In this example, there are N transport channels 500, 502 (only two are shown), each of which is connected to a respective turbo coder 504, 506 that performs channel coding. The coded outputs are input to an interleaver block 508 which generates a parallel set of interleaved outputs, which are preferably input to a modulator 510 which performs QAM mapping. The output of the QAM mapping modulator 510 is a set of modulated symbol streams. These are all input to demultiplexer 512 which routes symbols to any of the M Walsh sequence spreading functions 514, 516 (only two are shown). N and M are not necessarily the same. Each Walsh sequence spreader spreads each output of demultiplexer 512 by multiplying the data sequence by the sequence of chips in each Walsh sequence by adders (equivalently multipliers) 518, 520. Transport channel content is collectively added by adder 522 and a first long code cover is applied at 524. The RACH channel is indicated at 530. This undergoes Walsh spread by the Walsh-0 sequence. More generally, any Walsh sequence other than that used in other channels may be used. However, if Walsh-0 sequence is used effectively no Walsh spread is used and the RACH channel goes directly to multiplier 530 where the second PM cover is applied. The RACH channel content and the remaining content are combined at adder 532. The remaining components of FIG. 10B are the same as those previously described with reference to FIG. 3 and will not be repeated herein. Although two inputs are shown in adder 532, note that typically only one of them will be active at a given moment for a single UE. While the RACH is in use, the user is in an inactive state and therefore is not being transmitted on the data channels. Similarly, if the user is transmitting data, there is no need for RACH. In this embodiment, it can be seen that the content of multiple transport channels 500, 502 is coded and then interleaved before being spread by Walsh code sequences 514, 516. Blocks advantageously encoded with the appropriate block size selected at the encoders 504, 506 will be spread over the plurality of subblocks and these subblocks are hopped as a result of the hopping pattern 32.

mode -2 description

In another embodiment of the present invention, mode-2, preferably operated in combination with mode-1, provides a rate controlled high speed data burst with centralized scheduling transmission. Preferably, maximum power is used to transmit at the maximum possible rate in mode-2, thereby maximizing throughput. Mode-2 supports Time-Division Multiplex (TDM) multi-user service. Preferably, adaptive coding and modulation may be used to support the high speed data bus.

Rate controlled FDM / TDM-OFDMA is used for the transmission of multi-user high speed data bursts. Based on channel quality, QoS and traffic load for each UE, the base station scheduler schedules access for multiple users, including channel resource allocation and coding / modulation schemes for each individual UE. Each UE may be assigned a group of STC subblocks. The STC subblocks for each UE may hop in the time-frequency plane according to some particular pattern to obtain time / frequency diversity. 12 shows an example of STC subblock allocation between three UEs. However, if it is desired to reduce the frequency synchronization requirement between different UEs, it may be necessary to group STC subblocks assigned to a specific UE together to reduce user-to-user interference between STC subblocks for different UEs. The assigned STC subblocks may be considered as a dedicated high speed traffic channel.

In the example shown, there is a frequency band allocated for sufficiently wide mode-2 operation for three STC subblocks. These subblocks may be allocated in any manner for mode-2 operation. However, they are preferably assigned to contiguous blocks in both time and frequency. Thus, in the example shown, a first block 84 of STC subblocks consisting of two adjacent STC blocks at a frequency transmitted during four STC subblocks in time is shown. This is used for user 1 pilot subcarriers 93 and user 1 data subcarriers 94. Similarly, block 86 for user 2 pilots 95 and data 96 is shown. In this case, the block consists of a single STC subblock transmitted for five consecutive STC subblocks in frequency. The block of subblocks allocated for User 3 is denoted 88 with User 3 pilot subcarriers 97 and data subcarriers 98. Other groupings of STC subblocks are shown as 90 and 92.

Of course, it will be appreciated that the width of the band allocated for mode-2 operation is arbitrary and that the number of STC subblocks described above may fit into the band so defined. The size of the subblocks is of course variable, but preferably this is limited by the coherence bandwidth in frequency.

13 is a block diagram of transmitter functionality for mode-2 operation. The structure of this example includes a MAC interface 500 through which packets transmitted in mode-2 are received. The packet is then sent to a data scrambler 502, a CRC adding block 504, a turbo encoder 506, a rate matching block 508, a bit interleaver 510, an OAM mapping 512. And the symbol interleaver 514 and its output is input to the A-STC function 516 and the output it produces is multiplexed with mode-1 data as indicated by 518. It will be appreciated that this figure is a very specific example and that in general all of these blocks may not be required.

In the example of allocation of STC subblocks for mode-2 given in FIG. 12, the STC subblocks of a given user are allocated contiguously. In a preferred embodiment, the STC subblocks for mode-2 transmission are hopped at frequency as well. In this case, when a user is assigned an opportunity for mode-2 transmission, the assignment is hopping information so that each user can identify exactly where in their time and frequency their packets will be transmitted using the STC subblock. It needs to contain enough information to identify the.

15A shows an example of how mode-1 and mode-2 are combined in a transmitter architecture. A mode-1 output, generally indicated at 550, generated at the output of the hopping pattern of FIGS. The two outputs are both input to a multiplexer function 554 connected to the IFFT 556. This functionality will be implemented for each antenna. An example of how multiplexing occurs is shown in FIG. 15B. Here, the mode-1 input to the multiplexer 554 is indicated generally at 560 and the mode-2 input to the multiplexer 554 is indicated generally at 562. After multiplexing, input to IFFT function 556 generated by MUX 554 is indicated generally at 564.

Uplink Rate  Control

In order to realize rate control, the scheduler needs C / I information for UEs in all active states. However, due to interference variability, it is difficult to measure uplink C / I. A new rate control loop can be applied in coding / modulation selection for mode-2 transmission in the uplink. An example of uplink rate control and implementation is shown in the flowchart of FIG. 14.

Step 14-1. The base station measures signal strength of UEs in all active states based on received pilots from mode-1 transmissions.

Step 14-2. The base station schedules access of the initial multiple UEs according to these initial measurements.

Step 14-3. The base station signals the transmission resources and parameters to the UE.

Step 14-4. The UE listens to the downlink signaling channel to confirm the indication of the mode-2 transmission including the assigned STC subblocks and the coding / modulation primitive, and then starts the mode-2 transmission.

Step 14-5. The base station detects a block error rate of the received data from the UE. If the block error rate is higher or lower than the target value, send a command to the UE to reduce / increase the transmission rate by changing the coding-modulation primitive.

Step 14-6. The base station reschedules the user's mode-2 transmissions.

Step 14-7. The base stations send new rate control commands to the UE.

Step 14-8. The UE adjusts its coding-modulation primitive according to the rate control command.

In another embodiment, the UE may measure long term power strength from the serving base station and set up modulation using multilevel progressive coding and modulation feedforward transmission. It will be appreciated that other uplink rate control methods may be used. Alternatively, a static rate can be assigned to each user for mode-2 transmission.

Referring now to FIG. 1, a system diagram for an OFDMA system is shown. An OFDMA receiver and two OFDMA transmitters 602, 604, shown generally at 600, are shown. OFDMA receiver 600 will typically be a base station, and OFDMA transmitters 602 and 604 are wireless terminals such as mobile stations. The names used for these devices tend to be implementation specific. The function required at the network side may be called "network terminals". This may include base stations, Node-Bs, repeaters, or any other system device for which this functionality is to be provided. Also, downlink control channel (s) 652 from OFDMA receiver 600 to first OFDMA transmitter 602 and downlink control channel (s) 650 from OFDMA receiver 600 to second OFDMA transmitter 604. Is shown. The OFDMA receiver 600 is shown to include a RACH detection function 610, a mode-2 rate control function 612, a mode-1 power control function 614, and an OFDMA receiving function 616, which are multiple It serves to receive Mode-1 and Mode-2 data of users. Each OFDMA transmitter 602, 604 has a respective mode-1 function 618, 630, a respective mode-2 function 620, 632, a respective RACH function 622, 634, and a respective SACH function 624. 636). In the OFDMA receiver 600, it will typically be appreciated that many other functions will be required in a complete system. In addition, the illustrated functions may be implemented as separate physical blocks or may be integrated into a single design implemented software and / or hardware and / or firmware. The same is true for each of the OFDMA transmitters 602, 604. It should also be noted that not all embodiments require all of the functional blocks shown in FIG. 1. For example, in an embodiment that does not use RACH, RACH functional blocks 622, 634, and 610 will not be used. Note that the detailed structure of downlink control channels 650 and 652 is not provided. It will be appreciated that any suitable downlink channel may be used for this purpose.

Also shown within OFDMA receiver 600 is SACH allocation and monitoring function 617. Correspondingly, there are respective SACH generators 624, 636 in OFDMA transmitters 602, 604. Each OFDMA transmitter 602, 604 is also shown with a respective control channel receiver 640, 642.

What has been described above is merely illustrative of the application of the principles of the present invention. Those skilled in the art will be able to implement other devices and methods without departing from the spirit and scope of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims (5)

A wireless terminal for communicating through a shared orthogonal frequency division multiplexing (OFDM) band shared by a plurality of wireless terminals,
An access channel transmission chain configured to generate an OFDM access signal occupying a random selection slot selected from a plurality of slots comprising a frame,
Each slot includes a predetermined block of OFDM time-frequency,
And the access channel transmission chain is configured to generate the OFDM access signal by mapping a signature definition onto OFDM carriers based on a Peano-Hilbert plane filling curve. The method of claim 1,
A control channel receiver for receiving an identifier of the plurality of signature definitions for use in the coverage area,
And wherein the wireless terminal randomly selects one of the plurality of signature definitions and applies the signature definition to generate the OFDM access signal. 2. The wireless terminal of claim 1, wherein each slot comprises four OFDM symbols and there are sixteen different possible signature definitions. delete The wireless terminal of claim 1, wherein the access channel is overlaid on OFDM transmissions of other wireless terminals.

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